It should make sense in terms of his character so far in Season 5 that he’s not jumping up and down with glee at the prospect of meeting a flying alien who zips through the air to battle other aliens.
Only a couple episodes of Arrow Season 5 have aired so far, but one of the biggest elements of consistency has been Oliver’s reluctance to adapt to his new circumstances.
It evidently took five months of nudging from Felicity to convince Oliver to even consider expanding Team Arrow after the departures after Diggle and Thea and the death of Laurel.