So sorry for your sudden loss.
We lost a young Doberman to some sort of sudden Cardiac distress a few years ago.
Dobes are very prone to serious cardiac issues.
However, Greyhounds are not 'known' to have heart issues.
Our vet said that of all large breed dogs, Greyhounds are the healthiest...not much cardiac disease, no hip displasia/ Crutiate issues.
Bloat of course is something to be on the lookout for, as with all deep chested dogs, but your dogs case does not 'scream' Bloat to me.... We had a Dobe with Bloat once, too.
Hopefully, when you're ready for another canine companion, you will choose another Greyhound!!