Regardless of what is contained in the paper a standard ntp request datagram does contain a timestamp that represents the time the datagram was sent. From page 22 of the RFC:
Origin Timestamp (org): Time at the client when the request departed
for the server, in NTP timestamp format.
The answer to the question "Does ntp leak system time?" is "Yes. A standard ntp installation will leak local time to all of servers that have been configured for time syncronization."
RFC 5905: https://www.ietf.org/rfc/rfc5905.txt
Addendum: As far as the paper goes the reference to NTP is whether NTP skew adjustments affect the timer in question. From the paper
ICMP timestamps have a fixed frequency of 1 kHz. Their disadvantage is that they are affected by clock adjustments done by the Network Time Protocol (NTP) , which makes estimation of variable clock skew more difficult.