What does it mean to assess control risk too low?

It is regarding the actual risk rate as per the assessment of the auditor  and the risk tolerance rate that can be withstand.  If the Tolerance rate is on a higher side, it is a safety level and on the safer side.

Agree with Mr. Georgei assei answer.

Risk control risk assessment is very low (or so-called risk increased reliance) accepted by the auditor and that there would be safety ratio checker is designed to get them, and usually these risks be5% and the corresponding security level of95%

agreed with Mr georgei