Yes, it was. That is, it was a claim about a matter of fact.
> How would you prove that Americans were less or more productive than foreigners?
There's a number of possible operationalizations of productivity applicable to a Ph.D. program that are measurable and by which the issue could be addressed. Usually, the first thing to do would be to challenge the party making the dubious claim to both provide their operationalization and show data supporting the characterization.
It's quite possible that after that, the result would be that it would be fair to dismiss the claim as inadequately supported (although the mere fact that a single claim asserting a difference in performance based on nationality is inadequately supported does not, in and of itself, provide more than extremely weak evidence that the claim comes from racism.)
The party making the claim is using anecdotal evidence. They have no data. I do not think anecdotal evidence is good evidence for such a strong claim. This makes the claim an opinion and not factual. This is only my opinion.
> The party making the claim is using anecdotal evidence.
No, the party making the fact claim made a fact claim limited to a particular program they had been in, and has, as yet, neither provided evidence (or even an operationalization) for that claim not been challenged to do so.
> They have no data.
That may or may not be the case; it's perfectly fine to dismiss the claim due to lack of data, better to challenge the claimant to provide support for the claim. Calling it racism is as unsupported as the claim itself.
> I do not think anecdotal evidence is good evidence for such a strong claim.
The fact claim made was particularly limited (about productivity in one Ph.D. program—from which no further generalization was claimed), it wasn't a particularly strong claim. That said, sure, anecdotal evidence is inadequate to support it, but then, not even anecdotal evidence was provided, only the bare claim.
> This makes the claim an opinion and not factual.
A claim on a matter of fact doesn't become anything other than a fact claim because it isn't offered with adequate support.
Yes, it was. That is, it was a claim about a matter of fact.
> How would you prove that Americans were less or more productive than foreigners?
There's a number of possible operationalizations of productivity applicable to a Ph.D. program that are measurable and by which the issue could be addressed. Usually, the first thing to do would be to challenge the party making the dubious claim to both provide their operationalization and show data supporting the characterization.
It's quite possible that after that, the result would be that it would be fair to dismiss the claim as inadequately supported (although the mere fact that a single claim asserting a difference in performance based on nationality is inadequately supported does not, in and of itself, provide more than extremely weak evidence that the claim comes from racism.)