No that is not a rollover. Many employees have experienced a change of management companies. Sometimes these switches are due to a merger, an acquisition, or just to save money.
It is understandable that the old employer would like to see you transfer your funds to either your new employer, or roll them over into a IRA/Roth IRA. So it is not unexpected that they will take this opportunity to nudge you.
The thing that congress was trying to prevent were serial rollovers of IRAs. These people would use the 60 day window to have in essence a loan. Some would do this multiple times a year; always making sure they replaced the money in time.
The IRA One-Rollover-Per-Year Rule
Beginning in 2015, you can make only one rollover from an IRA to
another (or the same) IRA in any 12-month period, regardless of the
number of IRAs you own (Announcement 2014-15 and Announcement
2014-32). The limit will apply by aggregating all of an individual’s
IRAs, including SEP and SIMPLE IRAs as well as traditional and Roth
IRAs, effectively treating them as one IRA for purposes of the limit.
* Trustee-to-trustee transfers between IRAs are not limited
* Rollovers from traditional to Roth IRAs ("conversions") are not limited
Direct transfers of IRA money are not limited
This change won’t affect your ability to transfer funds from one IRA
trustee directly to another, because this type of transfer isn’t a
rollover (Revenue Ruling 78-406, 1978-2 C.B. 157). The
one-rollover-per-year rule of Internal Revenue Code Section
408(d)(3)(B) applies only to rollovers.
Note that the law doesn't mention 401K/403B or the federal TSP.
When the 401K changes management companies that is not a rollover.
