Not sure if he means there was something specific on his letter, but I am assuming we all got the same one.
On the form that you send back in for the deposit that came with the actual acceptance letter there was a general thing at the bottom stating that you are still required to complete all pre-reqs and that they will check official transcripts before matriculation.
Sounds pretty general to me so unless it named specific classes I would guess all of ours said that.
FYI here is the pre-req list from UNLV taken from their website:
All prerequisite courses and units listed below must be completed by June of the year of you intend to enroll. However, we highly recommend that applicants complete prerequisite courses prior to filing their application or taking the Dental Admission Test.
1 year of General Biology with lab
1 year of General Chemistry with lab
1 year of Organic Chemistry with lab
1 year of General Physics with lab
1 semester of Biochemistry
1 year of English
A minimum of the following units are needed upon application:
90 semester units, or the equivalent completed or in progress at an accredited college or university in the United States or Canada. (30 of the 90 semester units must be completed at a four-year institution).