You should basically never use a trans person's old name, gender, pronouns, etc. unless you absolutely have to. Treat them as if they've always been the person they are now.
There are of course some exceptions, like if they're not publicly out yet. You should never ever out someone else unless you have explicit permission. Or if there's just no other way to get the information across, e.g. if you're describing them to someone who only knows them pre-transition or if their legal name is required for something and they haven't changed it yet. If they explicitly told you they don't mind it's obviously okay too, but that's probably rare.
In short: Just keep in mind that bringing up their old identity is uncomfortable or even painful for many trans people and act accordingly.
Concerta and Ritalin are both methylphenidate medications. The "regular" Ritalin is instant release and Concerta is extended release. Because these two are the most well-known, "Ritalin" is often used as a synonym for "instant release methylphenidate" and "Concerta" for "extended release methylphenidate". As far as I can tell, descriptions like "long acting" (LA) and "extended release" (ER/XR) don't have clear definitions and are often used interchangeably.
So unless you're specifically talking about the brand name or want to get extra technical with potential differences in the formulation, the person you replied to is correct. Concerta and Ritalin LA are both extended release methylphenidate.