Yep. "Gender euphoria" is just code for sexual or narcissistic thrill.
They came up with the term partly to reframe it away from being a fetish (bad optics), but also because they were faced with a conundrum... It wasn't all that many years ago that troons commonly explained their condition as "being trapped in the wrong body" and suffering mental anguish because of it. People were generally sympathetic to this; it does sound horrible, after all. Plus,
body dysphoria exists, so why not gender dysphoria?
But eventually the troons who were just doing it for fetish reasons (AGPs) or as a fad (transtrenders) started speaking out.
"You don't need to be dysphoric to be trans!!"
They slowly drowned out the previous group - on Tumblr for example, this was seen in the conflicts between so-called Tucutes and Truescum. Nowadays, the troons who believe you need to be dysphoric to be trans are called "transmedicalists", and other troons hate them almost more than TERFs. The new Trans Orthodoxy says every troon is ~~valid~~ no matter what they identify as or whether or not they have dysphoria.
But to bring this back to the original point, a new problem arose.
"If you don't need to be dysphoric, then how do you know you're trans?"
Troons were now faced with this uncomfortable question, and shrieking at people who asked wasn't much of a long-term solution. "Gender euphoria" was eventually the answer they settled on. Even if you don't feel uncomfortable in your body, you can still be a ~valid~ troon if LARPing as the opposite sex makes you "feel good".
It's a clever solution, I have to admit. Gives them an answer for how they know they're trans, and at the same time gives them a way to deflect the fetish accusations. It's all bullshit, of course.