In Mecha’s flashback in Issue #2, Sonic and Knuckles’ eyes are conspicuously corrupted, preventing the reader from seeing if they are Classic styled or not. Likewise, Eggman’s appearance is in silhouette so as to obscure his outfit. I suspect this was a deliberate effort on the part of the writer and/or artist to include the classic designs (i.e. how they “should” look in that time period) without compromising Sega’s preferred branding. The same often occurred in flashbacks with classic Eggman in Archie post reboot. No, their quills and body sizes don’t quite match that of the classic designs, but I think the intent is apparent.