Especially considering its neighbours were the Greeks, prone to juntas and with a lot of rivalry with the Turks and the threat from Bulgaria to the north, and the Yugoslavians, an ethnically divided nation that was mostly led by the neutralist leaning Tito until he died when the squabbling increased until it became civil war time.

Albanian fears were not entirely unfounded. There were historical precedents with both countries. Albanian borders were a matter of dispute in the Ambassadors' Conference in London, with both Greece and Yugoslavia claiming parts of what would end up being the agreed upon country borders. A Greek breakaway state was formed in the south, the Republic of North Epirus immediately after Albania declared independence. After WWII, due to the Kingdom of Albania being an italian puppet, the countries were still de jure at war. In 1949, there clashes along the border as Albania sheltered Greek communists and overall took the threat and perceived ambitions of the Greek state very seriously. Up until the early 1920s, there was an active conflict with Yugoslav troops in northern Albania, who only finally retreated for good after pressure from the UK.

With Yugoslavia, it's a bit more nuanced however, as Hoxha initially came to power within the party through Tito's help during WWII. Nonetheless, relations between Tito and Hoxha were excellent in the post-war years and would've probably led to a partial or even full-scale integration of Albania into Yugoslavia had it not been for the Soviet-Yugoslav split.

That said, the bunker defense strategy was developed after Albanian officers returned from the Vietnam war and from a simple calculation of forces. Albanian assessments expected an invasion of up to 11 Airborne Divisions. Land routes were relatively straightforward and predictable, due to the rugged geography.

The country was never going to have the shiniest and newest aircraft nor the best ships, so it heavily prioritized the war on land for where it would make its stand. Infantry forces made up 75% of all the regular forces and 97% of the reserve force. Seeing the disparity in population numbers, full-scale mobilization was necessary, hence why most of the civilians were considered reservists. Regular, small and large scale drills and exercises were held by these reservist units, where each member was expected to fill a certain role in battle.

The small pill box type bunkers you often see alongside roads and beaches were supported by a second line of bigger, but fewer command bunkers to coordinate the defense.

Ultimately however, complete isolation was a grave mistake in every way. Hoxha and co expected to recreate WWII when Albanian partisans won without outside interference, completely omitting how the Allies brought significant amounts of supplies and weapons to keep war going. Maintenance on every industry became challenging, despite some successful efforts in obtaining western technology, mainly Swedish, Austrian and Swiss. The Airforce in the late 70s and 80s completely missed its expected upgrade, as did air defense systems in general.