That must have been a rule made at your store.
The official line was that any figures used in store on the gaming tables had to be painted.
However the quality of painting did not matter - not everyone can paint well and just because somebody couldn't was no reason they shouldn't be allowed to play..
Sounds like my local stores, and when i've been to play at other places - iirc even the tournament rules are generally just the use of 4 colours, which even the most basic paint job will manage.
As long as the models are painted in some manner, and recognisable as squads I've never seen the staff object to them.
I was in a local branch the other day and had to smile at one of the guys there helping a kid (probably about 10-12) who was looking to start playing, choose which army asking what models he liked etc and then helping him work out a small force list and I think as I left he was giving some painting tips.
Having said that, I found it really hard to keep a straight face when one of the other staff was dealing with my brother, and kept calling him "young man" (or something similar), I think the assistant was younger than my brother
What I have noticed, is that over the past 10 years or so the staff seem to have become less pushy/desperate

in my local stores. It used to be that if I went into one of the local stores i'd almost be pounced upon by an incredibly gushy assistant, now they tend to leave me alone after the initial "Do you need assistance" rather than going on about the latest models constantly.
It seems like (at least locally) a very different attitude, more professional/friendly without being overly matey/pushy.