Production server mysteriously using environment variables from development

I just deployed a website to production and a bizarre thing happened.

In my development machine, I had a .env file with environment variables that were being loaded into my python-flask program using python's load_dotenv module.

Naturally the .env file is in my .gitignore and therefore wasn't uploaded to github and, as such, was not pulled to my server.

As can be seen in the config.py of my flask app, there is absolutelly no way for the app to run correctly without any environment vars set:

import os
import datetime
from dotenv import load_dotenv
load_dotenv()

from celery.schedules import crontab


# Find the absolute file path to the top level project directory
basedir = os.path.abspath(os.path.dirname(__file__))

class Config:
    """
    Base configuration class. Contains default configuration settings + configuration settings applicable to all environments.
    """
    # Default settings
    FLASK_ENV = 'development'
    DEBUG = False
    TESTING = False
    WTF_CSRF_ENABLED = True

    BABEL_DEFAULT_LOCALE = 'en'
    LANGUAGES = ['pt-BR', 'en']

    # Settings applicable to all environments
    SECRET_KEY = os.getenv('SECRET_KEY', default='A very terrible secret key.')

    MAIL_SERVER = 'smtp.XXX.com'
    MAIL_PORT = 465
    MAIL_USE_SSL = True
    MAIL_USERNAME = 'noreply@app.com'
    MAIL_PASSWORD = 'XXX'
    MAIL_DEFAULT_SENDER = 'noreply@app.com'
    MAIL_SUPPRESS_SEND = False

    SQLALCHEMY_TRACK_MODIFICATIONS = False

    CELERY_BROKER_URL = os.getenv('CELERY_BROKER_URL')
    RESULT_BACKEND = os.getenv('RESULT_BACKEND')
    


class DevelopmentConfig(Config):
    DEBUG = True
    SQLALCHEMY_DATABASE_URI = os.getenv('SQLALCHEMY_DATABASE_URI')
    MONGODB_SETTINGS = {"host" : os.getenv('MONGODB_SETTINGS'), "connect": False}

class TestingConfig(Config):
    TESTING = True
    WTF_CSRF_ENABLED = False
    MAIL_SUPPRESS_SEND = True
    SQLALCHEMY_DATABASE_URI = os.getenv('SQLALCHEMY_DATABASE_URI')
    MONGODB_SETTINGS = {"host" : os.getenv('MONGODB_SETTINGS'), "connect": False}

class ProductionConfig(Config):
    FLASK_ENV = 'production'
    SQLALCHEMY_DATABASE_URI = os.getenv('SQLALCHEMY_DATABASE_URI')
    MONGODB_SETTINGS = {"host" : os.getenv('MONGODB_SETTINGS'), "connect": False}

Yet, once I set up everything in the server, the web app is running perfectly with development configs and saving all data to a cloud db, whose connection string was an environment variable.

I already checked all the files in the server and there is absolutely no .env file anywhere...

Does anyone have any idea how this might happen?

PS. I opted not to print all folder structure information to avoid making this post too long, if anyone believes that to be important I'll be happy to include the information.