Just checked the dates. The Superboy pilot was made in 1961 and the George Reeves series ended in 1959. So, it may have been intended as a prequel but probably not a "strict" one. I assume the series was set in the modern day but not specifically related to the time frame of TAOS.
Reeves committed suicide in 1959 so maybe the idea was to capitalize on the popularity of The Adventures of Superman series but go with a "different" character. Doing another Superman series so soon after his death might have been seen as disrespectful given how popular Reeves was in the role.
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