So is it correct to assume here "extradition" is not used in its most technical sense? It sounds like rather than actual extradition, these cases are about illegal activities in Thailand and the ensuing deportation.
There is no technical sense without a law/jurisdiction in context. The plain meaning of extradition is to surrender a person by one state to another state for reasons of alleged or convicted criminal conduct.
I would call a deportation an extradition if (a) the other state specifically requested it via official channels and (b) measures (arrests, detention, escorted transport etc.) are taken to ensure the person in question is effectively handed to the other state's authorities (and not just deported anywhere).
How does/can extradition work without extradition treaties?
As provided by the national law. While the U.S. law may require treaties for most extraditions, other countries may do things differently.
Canada, for example, permits a case-by-case agreement in its Extradition Act, which you could probably call a mini "treaty" since unlike in the US the executive authority alone is competent to enter into international agreements:
10 (1) The Minister of Foreign Affairs may, with the agreement of the Minister [of Justice], enter into a specific agreement with a State or entity for the purpose of giving effect to a request for extradition in a particular case.
Other countries like China do not require a treaty for an extradition to occur.
Article 15 Where there is no extradition treaty to go by, the Requesting State shall make a reciprocity
Extradition Law of the People's Republic of China
Apparently, Thailand is also one of such countries.
Section 8. The extradition shall commence with an extradition request
from the Requesting State.
The extradition request from the
Requesting State that has an extradition treaty with Thailand shall be
transmitted to the Central Authority. Where the Requesting State has
no extradition treaty with Thailand, the request shall be transmitted
through the diplomatic channels.
Extradition Act of Thailand
Now there is still the possibility that this is a simple deportation since the news sources or even police officers do not always use the technically correct terminology. But lack of treaties alone is not a basis to assume that it is not an extradition (and the existence of treaty is not enough to assume that it was an official extradition).