Altec is still an ADC for fantasy purposes. fantasy rules state that if a player who is already an LCS participant switches roles they must do so for a minimum of three games before they are eligible at that position. This prevents a player from gaining extra eligibility by only swapping for one week ad then swapping back. They also don't want to boot players off of a managers team because they chose those players when they were legal choices and removing them now is a punishment for that.
After a player has played 3 games at both positions, they will be eligible for BOTH designations and will count towards the position with fewer people on your roster. So, after next week if there are 2 supports on a roster Altec will count as an ADC. If there are 2 ADCs on a roster Altec will count as a support. It's a rule they have borrowed from other fantasy sports but imo in doesn't really apply well to LCS.