Because social media is social media, people took this as proof that something was going down, and that Hammer would be playing a role in DCEU.
With rumors about Green Lantern’s involvement in Justice League, fans simply connected the dots and claimed that Hammer was playing Hal Jordan, the most famous of all Green Lanterns.
In all fairness, this is exactly what happened with Rick Famuyiwa before he was announced as the director of The Flash movie, though he has since left the project.
Allow me to paint a more vivid painting of the situation: in the last two days, Geoff Johns, one of the main creative forces behind the DCEU, and Joe Manganiello, the actor portraying Deathstroke, both followed Armie Hammer on Twitter.