No, it doesn't disprove the research but they are known factors to contribute to the education. But the research doesn't exclude them but then goes on to attribute qualities to their immigration status. That is a false conclusion. And that false conclusion is being used denigrate people based upon skin colour - see thread title contents of OP and subsequent comments here and let alone other places. And more importantly being used as a pro-uncontrolled immigration argument.
You've just admitted there their immigration status is likely irrelevant and it could be due to other factors!
The research doesn't need to exclude those factors because that is not the aim of the research. The research aims to answer 2 very simple questions:
1) Does the 'London Effect' of higher average school performance exist.
2) What is the main reason for this.
The research effectively answers both questions at a high level using sound statistical reasoning. 1) The London effect is real and not only occurs in London but other cities like Birmingham. 2) The reason why London average school performance is so high is due to the high level of immigrant children that perform above average. Reasons why other cities like Birmingham are also above average are not part of the research questions. No claim is made that what happens in London is replicated nationwide. The main reason immigrant children in London appear to do well is attitudinal differences, nothing inherent about abilities. No reasoning is provided for these differences because it is not needed to explain the results.
Your logic seems completely lost in attempt to discredit the research. The research specifically doesn't claim there are intrinsic differences based on race and explicitly does not exclude external factors surrounding immigrant performance. You are trying to look for something that simply isn't there.
The research is not about why immigrant children perform above average, but why London is above average when measured across all school children. These are very different questions that you are trying and failing to collapse into one.
Here is a another example:
There is a large box containing 1000 apples. An average apple weighs 6oz, so the whole box should weigh 6000oz (375lbs), but when weighed it is actually significantly more, 6300oz. To find out why investigators examined the apples and found that 700 apples came from farmer Jones and those apples did indeed average 6oz but 300 apples came from farmer Smith and those apples weighed 7oz on average. Therefore the reason why the average of the 1000 apples is more than 6oz it is sufficient to simply explain that farmer Smith's apples weigh above average. There are likely reasons for this (additional sun/water/fertilizer etc.) but those factors aren't important in to answering the question. You seem very focused on the reasons why farmer Smith's apples are above average but all of those reasons like sun or water are already well understood and researched so it is not important to answering the question. No one is doubting that more fertilizer wont help both farmer's apples but that is irrelevant to the question asked: why is the box of apples above average, well some apples are from farmer Smith and his apples weigh more than average.
Of course there are many reasons why immigrant children in London do well, no one is discounting them. Those reasons are well researched independently so don't make valuable research in understanding the London effect. As you point out, those other factor explain the differences, not the skin colour or ethnic background. That is very important to note to prevent racial arguments, and the paper and the BBC article make that point very clearly. The same care has to be taken whenever discussing why, for example, black people are over represented in certain crimes. As long as you understand that conflating factors exist and don't assume differences are related only to skin colour or race then there is no issue in discussing these topics.
Finally, your argument that the paper is flawed seems to be that some people like the OP have made racists remarks (purportedly lighthearted). The paper specifically states there is no inherent differences and the authors can not be responsible for other peoples interpretations or statements when it makes this point very clear.
