To be fair, the aliens were pretty darn subtle, and Flight 714 was part of Hergé's "deconstruction" period (previously serious villains are made to look silly, later in Tintin and the Picaros, Tintin doesn't want to adventure and Haddock can't drink, etc).
Hergé did say that the reason he didn't want to make more science fiction/space travel stories after Destination Moon/Explorers on the Moon, was that he was so serious when doing those and making more serious (hard) science fiction would be boring and pointless, especially since he wouldn't have aliens (of the Bug-Eyed Monster variety).