There are always exceptions to the rule.
Without locality data, a "common boa" could be a mix of BCC and BCI then back to BCI. Its generally said BCC basin animals are the largest.
If the snake wasn't sexed, it could very well have been a female, however there are some very large males out there.
A male raised as strictly a pet, without and pheromones or breeding cues from a female in the same home could very well achieve a larger size.
My male is coming up on 5 years old. He's 6' 3" and he skips feeding from late October until right about this time of year.
I suspect he may hit 7 feet in his life.
He is a locality BCI. Barranquilla, Colombia locale.
Not a giant by boa standards, but you can see even over a year ago he had some size.
He was even larger by the end of last summer.
I suspect this summer he will fill out more and possibly add 3"-4". I like my animals lean and muscular, including our dogs.
Anyhow, if you like BCC and want a manageable snake, look into a male, Pokigron, Suri.
They do not typically attain the size of the other BCC, actually a male, Belem, Brazil boa would also fit the bill.
Again, this is all general.