The definition of complicity is -
the fact or condition of being involved with others in an activity that is unlawful or morally wrong.
Bit more complicated than the online dictionaries would have us believe, Connor. There might be something mischievous going on - probably is given the look in Andy's eye - but not, I'd wager, unlawful or otherwise.
In French a 'knowing glance' is 'regard complice', which might partly explain the use of 'complicity' in the tweet.
My interpretation is that Dubreuil is referring to the familiarity and understanding between Andy and Amelie - what Aileen referred to a bit further up at the 'bond' between them.