His exact words are "these differences may explain". He doesn't say "these differences may PARTLY explain". If I say that A may explain B, the reasonable implication is that A may fully explain B. So, yes, he does suggest that non-bias causes are the only causes.
Just to be clear: I don't think this makes any real difference. The reaction to his email would've been the same either way. But the fact remains that your interpretation of the quote isn't supported by the actual words he used.
Given this, I do not think it is a reasonable implication to turn "may explain" to "may fully explain."
It's hard for me to believe this distinction doesn't matter given that his critics always seem to specifically call out his "denial" of bias/discrimination when they want to paint him in the most unflattering light (even the NYT: https://twitter.com/jessesingal/status/1360626887035338752).
Nowhere does he suggest they are the only causes, or that bias/discrimination do not exist.