The meaning you posted is ok, but it corresponds to the adjective "arguable", not to the adverb "arguably", and it is one of the two possible meanings the adjective has. The other meaning of "arguable" different from the one you posted is: able to be supported with reasons. In this case, the adverb "arguably" would not mean "open to question".
New words, one handy idiom, and a 2-minute quiz — delivered to your inbox to keep your streak alive.