This appears to be a transcript of an interview with the person that has started the development on XMTP. The origin of the name is discussed, as being a combination of SMTP and XMTP.
I personally don't like the similarities of the naming (even in English pronunciation, the letters T and P are similar), but my first impression is not that it is malicious. It is going to be very, very confusing if this ever takes off. Given that there apparently is a source of investment, it could be argued that it already has taken off.
From a quick scan, the project seems to be in ernest development for a reasonable amount of months (but not years) now. The longer that it is active (and the longer that the name XMTP is cemented in as their identity) the less likely it will be that they can be convinced that the similarities between the names are going to hurt both technologies more than that it is beneficial to them.
If we do want to try and convince them to consider a name change, then I suggest we do so in the spirit of them too benefitting from a strong, not-to-be-confused-with-that-other-protocol identity, rather than from a get-off-my-lawn argument.