How did this flydubai 737NG get Max winglets?
These are called Split Scimitar Winglets and they are offered as an upgrade for some existing Boeing 737 NG series aircraft:

Split Scimitar Winglets are offered by APB for the 737-800 and 737-900ER and came into service in early 2014. They are available as a retrofit to existing winglet aircraft.
A set of SSWs weigh 133kg (294Lb) per aircraft but give fuel savings of 1.6% on sectors of 1000nm rising to 2.2% on sectors of 3000nm. This equates to an extra 65nm range.
The modification requires a trailing edge wedge, strengthened stringers and ballast weight but no changes to any avionics or the FMC. The base price cost for an upgrade from blended winglets to SSWs was $555,000 as of 2014.

(b737.org.uk)
According to this article (in German), Flydubai is using this upgrade since 2019:

The low-cost airline from Dubai is equipping 30 Boeing 737-800s with so-called Split Scimitar Winglets. The scimitars on the wing tips save thousands of liters of fuel.
[...]
The first aircraft of the low-cost airline from Dubai - it bears the A6-FEC registration - has already been equipped with the split wing tips.

(translated by Google)
It is not exactly the same winglet as the MAX has (see also Why do newer 737s use two different styles of split winglets?) as you can see in the following images:

(Flydubai Boeing 737 NG, aerotelegraph.com)

(Flydubai Boeing 737 MAX, photo by Nabeel A. Hashmi)