You have a straight face even though you are actually confused. You are a first year and a descendant of Merlin Emrys who disguised herself as a regular Muggle, you see the second years Tom is there who should be Riddle but from this distance you hear his name is Thomas Peverell not Tom Riddle.

You go forward and sit down, the hat or Alastair is talking incoherently, you accidentally meet Thomas' eyes for a few seconds but you immediately look away

Then Alastair shouted loudly "WELCOME BACK LADY RAVENCLAW, RAVENCLAW!" , your face immediately became alert, you could also see the Professors' faces turn a bit pale, not denying that another heir appeared, because the first one was Thomas Peverell or Tom.