What is racist here? The subject matter of a young black man leading two horses or just the title? There is nothing offensive about the painting itself, in my opinion, unless you assume that all black people were enslaved and that no living black person wants to see artwork depicting black people from that era.
One definition you can find online of page is “a boy being trained to be a knight in the Middle Ages.” A young man being trained for this position is certainly not an offensive concept.
The title would have been in Dutch when painted and then translated to English. It would have been translated at a time when that word was not considered offensive by black people.
“From the 18th century to the late 1960s, negro (later capitalized) was considered to be the proper English-language term for people of black African origin.”
We still have organizations in the US that use that term in the name. United Negro College Fund, for example. It is not a word we use today, of course. There is a debate about retitling art works with outdated, now offensive terminology included.
According to articles online, an aid saw the name plate and removed it then placed the lamp there to cover the mark on the frame where the plate had been removed.