Probably, it means the mystery of it is keeping the subconscious on the lookout for the number 27. When the number is in the environment, the subconscious tries to direct conscious attention to the fact.

The Why People See Certain Numbers All the Time article describes the mechanism.

Without your friend's numerology chart at hand, I'm unable to comment about the source of the history of seeing 27. The original seeing of the number may have been influenced by the chart numbers.

But chart influence generally doesn't make seeing a certain number persist for an extended period of time. It's likely that, after the second, third, or fourth seeing of the number, your friend wondered about it. Thus, setting up a mystery. The mystery ensuring the number continues to be noticed.

The number 27 represents, among other things, the energies of compassion and tolerance.