1) MongoDB Inc have made a "foreign data wrapper" for PostgreSQL which enables MongoDB databases to be accessed from within PostgreSQL.
2) This makes data in MongoDB databases accessible to existing analytics software for SQL databases, which is often made by companies with lots of money.
3) The CTO of SlamData Inc, which makes analytics software for NoSQL databases, thinks that MongoDB Inc shouldn't have done that.
tl;dr 3.0:
A company faces increased competition; isn't happy about it.
It enables MongoDB databases to be accessed from within PostgreSQL at a massive performance penalty compared to just storing your data in Postgres in the first place, because the particular kind of foreign data wrapper they're using has limited ability to make use of MongoDB's query functionality and has to literally load the entire contents of the database into Postgres for anything non-trivial. Which means you're better off just using Postgres. This is bad for MongoDB because their business model relies on people actually using MongoDB rather than the competition.
1) MongoDB Inc have made a "foreign data wrapper" for PostgreSQL which enables MongoDB databases to be accessed from within PostgreSQL.
2) This makes data in MongoDB databases accessible to existing analytics software for SQL databases, which is often made by companies with lots of money.
3) The CTO of SlamData Inc, which makes analytics software for NoSQL databases, thinks that MongoDB Inc shouldn't have done that.
tl;dr 3.0:
A company faces increased competition; isn't happy about it.