How does a Pokemon have a move outside of its type?
I mean, how do I have a Charmander (fire) with Scratch (normal), or a Zubat (poison/flying) with Bite (normal), or a Bellsprout (grass/poison) with Wrap (normal), or Dewgong (water/ice) with Iron Tail (steel)? It makes no sense. I have a Kingler (water) with Metal Claw (steel) and Vice Grip (normal).
Answers
Well, it is part of what makes the other games unpredictable.
Arcanine can learn grass moves if I recall, Tyranitar can learn ice moves, etc etc
It's more like 'does the pokemon have some physical attribute so that the move still vaguely make sense' more than 'are they of the same type'.
Like the pikachu Iron tail from the anime- Pikachu has a tail...and it just magically turns silver and becomes iron when ash says 'pikachu use iron tail!'
Same with blastoise learning flash cannon. It kinda has two cannons from his shell, so I suppose. It did use dragon pulse at some point against charizard lol
If you think about it...even for moves that are the same type, it really is quite ridiculous for a yellow mouse to summon a thunder attack is it LOL
I don't really know how seaking is depicted in the anime or other games (I'd imagine they have no competitive use) so I suppose niantic just wanted to troll.
Key word is 'vaguely' :)
I mean I have a fireblast slowking and a drill run fearow (flying bird digging into the ground causing spikes to come up and harm the enemy lmao)
But in the scenario of the poster above, metal claw kinda makes sense (I mean krabby has claws right) and vice grip is kinda like two claws smashing together lol
Many are about their "physical" capacities. For example, Zubat is a bat, vampires are a type of bat, and they are know for bitting people for their blood.
So, it has sense that such a bat can bite (even dark type), and any "draining life", like attacks Absorb/Mega Drain/Giga Drain (even Grass) or Leech Life (even Bug). In fact, any pokemon with sharp teeth can usually Bite/Crunch (even not Dark type).
Also, there's a buch of affinities between types, like many Waters can perform Ice attacks, Rock have resonances with Ground and Steel; Fighters are so hard and do Rock attacks, Bugs are inherent to Venom, talk about "burning Sun" lead to almost every Fire Pokemon can learn Solar Beam (yes, Grass), and Dragons are so mystic to like Fire, Water and Electric.
When a pokemon uses a move that shares a type with its own it gains STAB (Same type attack bonus). A Jynx using Ice punch will do more damage than a hitmonchan. There are advantages to using only STAB moves. There are also situations where you might want a move without STAB. Typically you're right in guessing that mons with corresponding moves are more valuable, but not always!