Why do I have to be the butler?
Well, you're the one who pinched the costume...
From when you were on 'Downton Abbey'.
They gave it to me!
Taking the premise of the Toobworld Dynamic as a fictional reality, what we see on our own TVs as 'Downton Abbey' is the actual presentation of the historical events of the Crawley/Grantham family in the early decades of the 20th Century. Any reference to 'Downton Abbey' as a TV show in other TV shows which shared the same dimension of 'Downton Abbey' would not be a Zonk. O'Bviously a TV show was made about those historical events, but it would not look the same as what we see in the show we watch.
The casting of Freddie Thornhill as a butler in the Toobworld 'Downton Abbey' TV show is a good sign that it is a different looking TV show from the one we see. As happens with "televersions" of historical figures as seen in our TV productions, they don't always look like the actual persons portrayed. (Richard Crenna as Ross Perot, anyone?) And such would be the case with whichever butler was played by Freddie Thornhill.
And I think I knew who he was playing. Freddie only made a guest appearance on the program, so he would not have been a member of the regular cast of servants at the Abbey. (And most of those were younger men. Carson was the only one of an approximate age to how Freddie looked, but again, he was a major character.)
Instead, I think Freddie was playing Stowell as seen in the "Moorland Holiday" episode of 'Downton Abbey'. He was the butler to the Aldridge family and sometimes he was insolent to Lord Sinderby, probably because of his employer's Jewish heritage.
Freddie looks nothing like the historical Stowell and he was certainly older than the butler was in 1924. (Freddie was almost a decade older when he played the role.) But it's the only role of some meat to it which could have fit the aging, self-centered thespian.