Please note, this is an educated opinion and not fact.
1. PSE is not a popular target for local terrorist outfits in Pakistan, they prefer schools, military, police, government installations.
2. KSE-100 index gain 501 points closing at 33,939 compared to sinking global markets. Economic instability has always been a weapon used by our neighbour. Especially when Monday is the opening day for trade and markets were expected to rally this week even further following the recent news of easing of loan terms from Beijing.
3. Lets examine the
TTP: Tactics, techniques and procedures used in this attack. A deliberate feint followed by a coordinated two man team using rifles to assault a vital installation. This is a signature MO of neighbour sponsored terrorist outfits, as we witnessed in the Mehran AFB attack.
Two assailants neutralised by Pakistani security forces.
Notice the pattern for shrapnel spread on this guard post barrier. As the above image will show the impact created is not the typical type of damage you will expect to see from an AP or HE grenade, to illustrate this point:
The fragmentation parts of a Pineapple style grenade creates square projectiles.
Where as soviet and US style 67 and 20mm grenades create projectiles like the ones seen below:
Furthermore we can compare the picture of the guard post attacked with an undisclosed "explosive" device and compare the frag impact to a grenade
Now compare this to an IED attack vs a police bus, IED containing 5kg of ANFO and 30,000 6mm and 8mm ball bearings.
I'd put good money on this being some ratbag funded by New Delhi. 
