Is micropachycephalosaurus the smallest dinosaur

No.

There is actually a debate over which is the smallest dinosaur, because fossilisation and weathering can cause shrunken features and missing details.

The top 5 argued smallest dinosaurs are:

• Ohmdenosaurus- 4 m (13 ft)
• Blikanasaurus- 5 m (16 ft)
• Magyarosaurus - (17 ft)
• Europasaurus - 6 m (20 ft)
• Vulcanodon - 6.5 m (21 ft)

Also, bear in mind that not every dinosaur has yet been discovered.