An Easter egg in Smallville actually creates a canon issue for its version of the Flash, and it highlights just how poorly the character was treated on the show. For an origin story that focused itself entirely upon Clark Kent's younger years leading up to his emergence as Superman, Smallville certainly branched out into the wider world of the DC universe far more than might have been expected. This was actually one of the show's greatest strengths; by showing how Clark worked with or against not just Superman's supporting characters and villains, but other heroes too, Smallville was able to explore almost every facet of his character.
By telling a story that takes place as part of a wider universe, Smallville helped shape modern superhero movies by setting the stage for shared cinematic universes. To that end, Smallville not only showed Clark becoming Superman, but it also showed the formation of an early Justice League. The team consisted of Clark, Oliver Queen/Green Arrow, Arthur Curry/Aquaman, Victor Stone/Cyborg, and Bart Allen/Impulse. In the comics, Bart Allen goes on to become the fourth Flash, and, as the Smallville character's powers are very much in line with the comics, it follows that the show's version is on a similar career trajectory.
However, in Smallville season 4, episode 5, "Run", Clark track Bart to a hotel room, where he discovers a number of fake IDs with the names Jay Garrick, Wally West, and Barry Allen - obvious references to the three people to assume the identity of the Flash before Bart. It's also made clear that Smallville's Flash is Bart Allen, but this makes the use of those particular names as aliases a curious choice. It implies that Bart knows the previous Flashes, but the fact that this is never properly explained or explored highlights how Smallville failed his character.
Impulse's Fake IDs In Smallville Point Out How The Show Failed The Flash
By referencing the other people to assume the mantle of the Flash, Smallville seemingly confirms their existence within its world. This is later made canon by a flashback that features Jay Garrick, but his connection to Bart (and both Wally West and Barry Allen) are never explained. The show itself never makes any genuine attempts to explain Bart's backstory or legitimize him as its version of the Flash, and is content for him to exclusively use the codename Impulse.
By keeping Bart Allen as Impulse, Smallville showed that the Flash wasn't a major consideration. The show briefly touched on the speedster's story and powers, but nothing was ever truly established until the comic continuation, Smallville season 11. As the show did at one point reference the three Flashes that came before Bart though, Smallville appears dismissive of Bart's claim to the mantle.
The Easter egg is mostly a nice touch, as it fleshes out Smallville's world at hints at even more depth and history than the show itself was able to explore. However, by referencing Bart's predecessors in such a subtle way and then all but dropping his story altogether, the Easter egg does little more than highlight how Smallville fails to do the character justice. Ultimately, even a single episode exploring Bart's origins and providing a clearer hint at his future as the Flash would have sufficed, but it simply wasn't something that Smallville opted to do.