Parsing his sentence for tiny nuances like that isn't very helpful IMHO, but I'll indulge you.
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.
If a holistic reading of Damore's memo reinforced the idea that he was trying to deny the possibility of bias/discrimination, then perhaps you could call your inference a "reasonable implication." But the opposite is true, Damore repeatedly tries to represent the uncertainty and possibility of multiple causes. This is true even in the single sentence you quoted.
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).
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.