It's not unusual for Matt to spend his evenings in the Specials HQ. He knows he can often find Lydia there and it's nice to not always be on his guard. He always takes a circuitous route to HQ, making certain that he's not followed (though he knows he could have Lydia bring Gucci if he really wanted). It's good for him to walk around the facility. It allows him to get accustomed to the place and get a grasp on the social situation here. If anyone accuses him of being somewhere he's not wanted or that he shouldn't be, he falls back on his blindness.

In any case, he eventually gets to HQ and knows the moment he steps inside that Lydia is there. He smiles and tap=tap-taps his way over to where she's working. He knows that she's doing something with chemicals (he can smell them) but has no idea what.

"Someone's hard at work here. Either that or I should never trust your cooking."