

this is a joke, right?
a default keyboard combination does not have such a meaning. they don’t want to “dress as proprietary software”. probably the creators were used to using that other combination, or they decided that it could be worth to keep the keyboard mapping similar to a very popular graphics editing software, irregardless of whether it is proprietary or open source.
don’t worry! the freedom is yours to rebind that button to whatever you want.
the address there can be faked, maybe your email client did not warn about it. if you can check the mail’s headers (maybe easier on desktop), look at all the addtesses you see in there and if thry seem suspicious.
also check the link they sent. Don’t open it, but copy it only.