Japan police stop

Hey all. Slightly unusual question. We were just driving a hire car on the highway in japan and a police car came up behind us with lights and sirens on. We weren't sure if they wanted to pull us over but we saw a service centre in 800 meters so we decided to pull in there so as not to stop on the highway. Before we got there the police car pulled over to the side of the road and didn't follow us. Any idea what they might have been doing? Why they stopped? We were the only car near them and they stayed behind us without overtaking.. Any advice would be great.

No idea ...
but was it not common to slow down and pull to side (to give way) when you see ambulance/police car that put on siren and flashing light ?

Patrolling police car normally put on their flashing lights, without siren.
You know you'll be in trouble/pullover if they call you out on loudspeaker with flashing lights and siren.

Pulling into the SA was a good idea.

Lights on - normal.
Siren - less usual if they were not really doing anything.
And you know you're in trouble when they get on the loud-speaker - that is the clear give-away something is up. Saw it yesterday - very effective.