Well, it depends on how you view the term racist.
I'm push to see how it doesn't fit this pretty basic criteria (wiki).
Racism is behavior or beliefs motivated by racial stereotypes, it generally includes practices of racial discrimination, and ideologies of racial supremacy and hierarchy.
Some sources emphasize that racism involves the belief that different racial groups are characterized by intrinsic characteristics or abilities and that some such groups are therefore naturally superior to others, or follow practices that discriminate against members of particular racial groups, for example by perpetuating unequal access to resources between groups.
Then would it not be easy to say, "mature tenant wanted" (in regards to behaviour) as opposed to partaking in age discrimination?.
Regardless of the motivation, specifying a criteria which excludes an entire social group based entirely on skin colour is racism.
Thinking one race is superior to another is in one form, but it's not the only indicator.
Denying one person which you allow another (based purely off race) is also.
Don't get me wrong, I don't think it can be enforced & I'm certain they will continue to do it by changing the language used if it was cracked down on, neither do I believe it's something the government can fix.
My point is, it's racism no matter how you spin it.